Digital radiographic volume imaging provides three-dimensional (3-D) images that have been reconstructed from a series of 2-D images taken over a succession of angles of the X-ray source relative to the detector. Acquisition of the 2-D projection images used for cone beam CT employs a large-area digital detector, such as a digital radiography (DR) detector that is typically used for conventional single projection radiography.
Computed tomography (CT) systems, such as cone beam computed tomography (CBCT) or cone beam CT systems offer considerable promise as one type of diagnostic tool for providing 3-D volume images. Cone beam CT systems capture volume data sets using a high frame rate flat panel digital radiography (DR) detector and an X-ray source. The X-ray source and detector are typically affixed to a gantry that revolves about the object to be imaged, with the X-ray source directing, from various points along its orbit around the subject, a divergent cone beam of X-rays toward the subject. The CBCT system captures projection images throughout the source-detector orbit, for example, with one 2-D projection image at every angular increment of rotation. The projections are then reconstructed into a 3D volume image using various techniques. Among the most common methods for reconstructing the 3-D volume image are filtered back projection (FBP) approaches.
A factor that affects the quality of volume reconstruction relates to the number of 2-D projection images acquired. Projection images are generally obtained at evenly spaced angular increments; having images at a sufficient number of angles helps to provide enough data to minimize or eliminate aliasing effects such as view aliasing artifacts, typically appearing in the form of regularly spaced streaks, and other image processing problems.
Each projection image, however, requires exposure of the patient. Thus, although having more 2-D projection image data is advantageous for 3-D image reconstruction, it would be preferable to reduce the number of 2-D projection images that are obtained, thereby reducing exposure risks to the patient. In addition, it would be beneficial to reduce the required scan time in order to help reduce image reconstruction problems due to patient motion.
Thus, there would be advantages to volume imaging methods that can obtain sufficient projection image content for accurate volume reconstruction while reducing dosage requirements.